Recently there has been much research to develop MEMS devices, that is mechanical devices having dimensions of micrometers (for example, having a maximum diameter no more than say 10 millimetres). Some such devices include an element which rotates around a shaft attached to a stator. One such device is shown in cross-section in FIG. 1, and includes a rotor 101. A through aperture 103 is formed in the rotor 101, and a shaft 102 is then inserted into the aperture. The shaft 102 is connected to a stator 104 which carries copper windings 105. The rotor 101 includes cavities which are filled with a metal yoke layer 106 and thicker magnetic layer 107.
In such a system a contact bearing is not suitable, and to minimise contact resistance it is preferable that the shaft 102 has a wide clearance from the sides of the aperture 103. However, a small clearance is required in order to avoid eccentricity in the rotation of the shaft 102. As a consequence, the contact surfaces at which the moving parts touch each other experience frictional resistance, and are liable to abrasion.